VARIABILITY OF 13 ISOZYME LOCI IN THE USDA SOYBEAN GERMPLASM COLLECTIONS

Surveys of variability at loci that condition simply inherited, phenotypically neutral characters can be used to investigate relationships among accessions in germplasm collections. We performed a survey of isozyme variability among 1005 domesticated soybean [Glycine max (L.) Merr.] and 258 wild soybean [G. soja (L.) Siebold and Zucc.] accessions from the USDA soybean germplasm collection. By using eight activity stains, we detected polymorphisms conditioned by 13 isozyme loci. The average gene diversity of the Asian G. max accessions in this study was 0.198, while that of the G. soja accessions was 0.235. The relatively high variability of this set of loci made it possible to investigate relationships among groups of accessions from six diverse geographic regions in Asia: China, India and South-Central Asia, Japan, Korea, Manchuria-Siberia, and Southeast Asia. The G. max and G. soja accessions fell into two separate groups, based both on genetic distance and canonical discriminant analysis. Publicly developed soybean cultivars released for production in North America clustered with the G. max accessions from northeast Asia. The group of accessions from India and South-Central Asia was the G. max group most closely related to the G. soja accessions and may include some primitive agronomic types. The group of G. max accessions from Southeast Asia stood out from the other G. max groups. This difference was due to high frequencies of the Aco3-b, Dial, and Enp-a alleles among accessions in Maturity Groups VII through X. The accessions in the later maturity groups may represent a distinct population, relative to the accessions in the earlier maturity groups.